Our invention deals with condensation nuclei particles detection. Since World War II, interest has been directed cyclically to various uses for condensation nuclei for detection purposes. It involves the phenomenon of using humidity to condense or form fog or cloud components upon and around small particles in the atmosphere. Once this localized fog or cloud forms, detection can be had therefrom. Ninety-five percent of discernible condensation nuclei that can be beneficially used in this manner are the results of some form of combustion. These particles are generally submicroscopic in size and will act as nuclei for the condensation of water and therefore these particles are often referred to as Condensation Nuclei (CN). When conditions of supersaturation are properly controlled, this condensation will occur rapidly and particles as small as 0.001 um diameter will grow to water droplets that are five to ten um in diameter. This growth phenomenon provides an extremely sensitive technique for the detection of submicroscopic sized particulate matter in the atmosphere. The concentration of water droplets produced by condensation is easily measured by a standard light-attenuation or light-scattering photoelectric system.
Detection of the submicroscopic particles found first use in World War II when atmospheric monitoring occurred for submarine detection. In this instant, the then only internal combustion engine made of submarine power released these submicroscopic particles during the period of surfacing and battery recharging. Hence, vapor trails were created and sought by detection.
In the 1960's, the Army made application of "CN" detection by way of personnel detection, i.e., invisible plumes of "CN" caused from engine exhausts, fires, and other forms of combustion in and about personnel.
In the time frame of our invention activities, "CN" detection methods have also found their way into endeavors extending from monitoring computer rooms to air pollution and air quality measurement methods. Along with these above mentioned uses of "CN" detection, numerous detector units have been developed of varying designs. Each of these type units have in common the Aitken nuclei counter principle. This is a well known process of taking a sample, humidifying it, expanding it, and measuring the concentration of condensation nuclei at a rate of several times per second.
In an Aitken nuclei counter device, a sample of air is subjected to rapid expansion to a low pressure. The drop in temperature during adiabatic expansion induces condensation of the humidity in the air around the condensation nuclei. The size of particles upon which condensation occurs depends upon the degree of supersaturation caused by the expansion; and, to some extent, on the chemical properties of the particles. All of these Aitken type devices use expansion to produce supersaturation and the attendant growth of the nuclei by condensation.
The Aitken method is a non-continuous flow sample type process which requires complex, cumbersome and expensive mechanical apparatus of high vacuum capacity which is plagued by a multitude of maintenance problems. Most of the apparatus is of the non-portable type, thereby hampering detector utility.
A long-felt need has existed for a small, compact "CN" unit and process with constant measuring features. However, until our invention, no success has been had in this area. It appears that the Aitken principle has set the parameters for the field and impeded innovation thereby.